A projector causes a video apparatus such as liquid crystal to transmit light from a light source to provide an image on a desired screen or the like. Thus, distortion may occur in the projected video in a case where a direction of the light from the light source is caused to face the screen.
For this reason, it is necessary that arrangement of the projector and the screen is generally adjusted so as not to distort the projected video when to install them. Alternatively, it is necessary to adjust distortion of displayed video by using a distortion correcting function or the like of the projector.
On the other hand, a technique called as projection mapping is attracting attention in recent years. In the projection mapping, video is projected to an object placed in the real world by using a video projecting apparatus such as a projector.
In the projection mapping, it is necessary to project video not only to a flat screen caused to face the projector, but also to a screen that is not caused to face the projector and is placed with a predetermined angle or an object with concavities and convexities.
As described above, in a case where a projection target such as a screen is not caused to face the projector, that is, in a case where an optical axis of the projector and a surface of the projection target cross at right angles with each other, geometric distortion occurs in the projected video.
For example, in a case where a screen is installed so that an upper side of the screen is near the projector and a lower side thereof is far from the projector and video with a square shape is projected from the projector, so-called trapezoidal distortion occurs in which the video is projected so that the upper side of the square is shorter than the lower side thereof.
In fact, the similar phenomenon occurs not only in a vertical direction, but also in a horizontal direction. Thus, the video with a quadrangle, which is projected from the projector, is projected as a distorted square that does not have parallel sides.
In this case, by applying geometric correction of a reverse direction to video to be projected so as to counteract this distortion in advance, it becomes possible to correctly display the video as a square. This geometric correction, that is, the geometric conversion is called as perspective conversion or projective conversion, and can be realized by matrix calculation. In order to calculate this matrix, it is necessary to obtain information on a shape and a position of a projected object by any means.
One technique for realizing this is described in Japanese Patent Application Publication No. 2013-192098 (see Patent Document 1), for example. This Patent Document describes that: a marker becoming a reference is projected from a projector; a shape of a projection target is obtained by photographing the projection target by a camera of a smartphone; distortion is calculated from obtained video; and the distortion is subjected to reverse correction.